Basic Guide On Carbon Fiber For Bikes

Been thinking about springing for a new bike? Wondering whether carbon fiber would be a good choice for the kind of riding you do? Want to learn more about carbon fiber bikes and their properties? If so, read on…

A Cornucopia of Carbon

A quick stroll through any bike store or a visit to an online retailer (preferably Performance Bicycle in either case) will bring you into contact with more carbon fiber bikes – road and mountain - than you can shake a seatpost at. So many, in fact, that anyone who didn’t know better would never guess that the proliferation of carbon fiber bikes is a relatively recent phenomenon. Since the introduction of the world's first all-carbon bicycle frame by Kestrel in 1986, the application of carbon fiber technology in bicycle manufacturing has finally reached a critical mass, with the majority of the major bicycle brands now offering a carbon fiber line.

Carbon Close-Up

Technically speaking, the bikes we refer to as carbon fiber bikes are really carbon fiber-reinforced composite bikes. The composite consists of individual carbon filaments that are bundled together, woven into sheets and then impregnated with a resin. Multiple layers of these sheets are arranged in molds to form the different parts of the bicycle frame. When the resin hardens, the individual parts are bonded together to form the complete frame.

The relative orientation of the individual carbon plies affects a frame’s stiffness, strength and compliance characteristics. Unidirectional layups (all strands running in the same direction) are incorporated to handle specific loads, while quasi-isotropic layups (each ply oriented in a different direction) are used when overall strength is desired. The ability to easily manipulate physical properties along different parts of the frame’s structure via the use of different layups allows frame makers to fine-tune a carbon fiber bike’s performance characteristics to a degree not possible when working with steel or aluminum.

The Scoop on Modulus

It’s almost impossible to read a description of a carbon fiber bike without running across a reference to “modulus.” A measure of how much a given material deforms under stress (in essence, its stiffness), modulus of elasticity is rated as low, standard, intermediate or high. Carbon fiber’s modulus of elasticity is manipulated during processing. In the manufacture of carbon fiber, an industrial material called polyacrylanitrile fiber is heated to extremely high temperatures, driving off all of the elements except carbon. If the fibers undergo additional heat processing, the resulting modulus becomes increasingly greater.

Standard modulus carbon fiber has a modulus of 33 million pounds per square inch (33 MSI fiber). Further heat processing produces 42 MSI fiber, which has a smaller diameter, permitting more individual fibers to be packed into a given space. This is commonly referred to as intermediate modulus fiber. Yet more processing yields even denser, stiffer fibers. These high modulus fibers have a rating of 55 MSI and higher.

Believe in the Weave

Woven carbon fiber is also available in various filament counts, based on the number of individual filaments that are bundled per strand. Filament counts range from 1,000 filaments per strand (1K weave), up to 320,000 or more filaments per strand (320K weave). 3K, 6K and 12K weaves are the most common carbon fiber weaves used in bicycle frame manufacturing. As you might guess, the more strands per bundle, the stronger the resulting weave. Of course, the increase in strength comes with a corresponding increase in weight, as well. On the positive side, because the larger weaves are easier to produce, the material costs less - as do the bikes that are made with it.

Benefits to Go

The beauty of carbon fiber is that it combines strength and light weight, and allows the designer to manipulate both stiffness and compliance to produce frames with the desired levels of efficiency and comfort. High-performance road race frames, for example, are designed to maximize energy transmission during pedaling. Using high-modulus carbon fiber, these ultra-stiff and lightweight frames often sacrifice comfort in the name of overall efficiency. Carbon fiber bikes aimed at the casual recreational rider, on the other hand, use lower modulus fibers to good advantage, providing enhanced compliance for better shock damping and a more comfortable ride - albeit at a greater weight. Between the two extremes, carbon fiber technology offers a broad performance spectrum that’s unmatched by other frame materials.

More Variety, More Choice

The wide variety of carbon fiber grades and layup options available to bike manufacturers means cyclists have many choices, making it easier than ever to find a bike that offers the perfect combination of performance, stiffness, comfort, weight and cost to best suit a particular type of riding, individual preferences and budget. That makes it possible for virtually any cyclist - from the weekend warrior to the serious competitor - to take advantage of the benefits of carbon fiber technology and enjoy a great ride.